1. Technical Field of the Invention
The present invention relates to power supplies used in devices such as Universal Serial Bus On-the-Go devices, integrated circuits and related methods.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radios, pagers, cellular telephones, computer memory extensions (commonly referred to as thumb drives), etc. Each of these handheld devices includes one or more integrated circuits to provide the functionality of the device. As an example, a handheld audio player may include multiple integrated circuits to support the storage and playback of audio files in order to produce an audio output that is delivered to the user through speakers, headphones or the like. Given the handheld nature of these devices, small size, low weight and long battery life can typically be important considerations in their design.
Many such handheld devices provide an interface, such as a Universal Serial Bus (USB) interface governed by the USB 2.0 specification, for coupling the handheld device to a traditional host device such as a computer, docking port, etc. In a USB On-the-Go (USB-OTG) mode, two USB-OTG devices, such as two handheld devices, can be coupled together. In this fashion, data can be exchanged between two handheld devices, with one device acting as the host and the other device acting as the peripheral. While in the USB-OTG host mode, the handheld device must be capable of supplying power, 5V and up to 8 ma, to the USB-OTG peripheral device. Prior art designs use a switched capacitor charge pump circuit to generate the supply voltage based on a battery. However, the voltage generated by these circuits drops as the battery discharges.
The need exists for a power source for supplying more stable power to external devices that can be efficiently implemented in a handheld device.